title: Extensive mitochondrial introgression in North American Great Black-backed Gulls (Larus marinus) from the American Herring Gull (Larus smithsonianus) with little nuclear DNA impact.
abstract: Recent genetic studies have shown that introgression rates among loci may greatly vary according to their location in the genome. In particular, several cases of mito-nuclear discordances have been reported for a wide range of organisms. In the present study, we examine the causes of discordance between mitochondrial (mtDNA) and nuclear DNA introgression detected in North American populations of the Great Black-backed Gull (Larus marinus), a Holarctic species, from the Nearctic North American Herring Gull (Larus smithsonianus). Our results show that extensive unidirectional mtDNA introgression from Larus smithsonianus into Larus marinus in North America cannot be explained by ancestral polymorphism but most likely results from ancient hybridization events occurring when Larus marinus invaded the North America. Conversely, our nuclear DNA results based on 12 microsatellites detected very little introgression from Larus smithsonianus into North American Larus marinus. We discuss these results in the framework of demographic and selective mechanisms that have been postulated to explain mito-nuclear discrepancies. We were unable to demonstrate selection as the main cause of mito-nuclear introgression discordance but cannot dismiss the possible role of selection in the observed pattern. Among demographic explanations, only drift in small populations and bias in mate choice in an invasive context may explain our results. As it is often difficult to demonstrate that selection may be the main factor driving the introgression of mitochondrial DNA in natural populations, we advocate that evaluating alternative demographic neutral hypotheses may help to indirectly support or reject hypotheses invoking selective processes.
authors.affiliation: 1] UMR7205 Origine, Structure et Evolution de la Biodiversité, Département Systématique et Evolution, Muséum National d'Histoire Naturelle, Paris, France [2] Service de Systématique Moléculaire, UMS 2700, Muséum National d'Histoire Naturelle, Paris, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Pons
authors.affiliation: Department of Vertebrate Zoology, Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sonsthagen
authors.affiliation: Department of Vertebrate Zoology, Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
authors.forename: C
authors.initials: C
authors.lastname: Dove
authors.affiliation: CNRS-UMR5175 CEFE, Centre d'Ecologie Fonctionnelle et Evolutive, Montpellier Cedex 5, France.
authors.forename: P-A
authors.initials: PA
authors.lastname: Crochet
mesh_terms: D000818:Animals; D046091:Charadriiformes / Q000235:genetics*; D004272:DNA, Mitochondrial; D005060:Europe; D019143:Evolution, Molecular; D005828:Genetics, Population; D006239:Haplotypes; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D009656:North America
chemical_list: D004272:DNA, Mitochondrial